1. Field of the Invention
The present invention relates to an active matrix display device in which a thin film luminescent element such as an EL (electroluminescence) element or LED (light emitting diode) element, that emits light by application of a driving current to an organic semiconductor film, is driven and controlled by a thin film transistor (hereinafter referred to as a TFT).
2. Description of the Related Art
Active matrix display devices using current-controlled luminescent elements such as EL elements or LED elements have been disclosed. Since luminescent elements used in display devices of this type are self-luminescent, backlights are not required, unlike in liquid crystal display devices, and the viewing angle dependence is small, all of which are advantageous.
FIG. 13 is a block diagram of an active matrix display device which uses organic thin-film EL elements of the charge-injection type as described above. In an active matrix display device 1A shown in the drawing, on a transparent substrate 10, a plurality of scanning lines gate, a plurality of data lines sig extending in the direction orthogonal to the direction of extension of the scanning lines gate, a plurality of common feeders corn which run parallel to the data lines sig, and a plurality of pixels 7 which are formed in a matrix by the data lines sig and the scanning lines gate are arrayed. A data side drive circuit 3 and a scanning side drive circuit 4 are formed for data lines sig and scanning lines gate, respectively. Each of the pixels 7 includes a conduction control circuit 50 to which scanning signals are supplied through the scanning line gate and a thin film luminescent element 40 which emits light in response to picture signals supplied from the data line sig through the conduction control circuit 50. In this example, the conduction control circuit 50 includes a first TFT 20 in which scanning signals are supplied to a gate electrode through the scanning line gate, a storage capacitor cap for retaining picture signals supplied from the data line sig through the first TFT 20, and a second TFT 30 in which picture signals retained by the storage capacitor cap are supplied to a gate electrode. The second TFT 30 and the thin film luminescent element 40 are connected in series between an opposing electrode op (which will be described later in detail) and the common feeder com. The thin film luminescent element 40 emits light in response to a driving current applied from the common feeder com when the second TFT 30 is ON, and the emission is retained by the storage capacitor cap for a predetermined period of time.
With respect to the active matrix display device 1A having the configuration described above, as shown in FIG. 14 and FIGS. 15(A) and 15(B), in any pixel 7, the first TFT 20 and the second TFT 30 are formed using an island-like semiconductor film. The first TFT 20 has a gate electrode 21 as a portion of the scanning line gate. In the first TFT 20, the data line sig is electrically connected to one of the source and drain regions through a contact hole of a first interlayer insulating film 51, and a drain electrode 22 is electrically connected to the other of the source and drain regions. The drain electrode 22 extends toward the region in which the second TFT 30 is formed, and a gate electrode 31 of the second TFT 30 is electrically connected to this extension through a contact hole of the first interlayer insulating film 51. In the second TFT 30, an interconnecting electrode 35 is electrically connected to one of the source and drain regions through a contact hole of the first interlayer insulating film 51, and a pixel electrode 41 of the thin film luminescent element 40 is electrically connected to the interconnecting electrode 35 through a contact hole of a second interlayer insulating film 52.
As is clear from the FIG. 14 and FIGS. 15(B) and 15(C), the pixel electrode 41 is formed independently in each pixel 7. On the upper layer side of the pixel electrode 41, an organic semiconductor film 43 and the opposing electrode op are deposited in that order. Although the organic semiconductor film 43 is formed in each pixel 7, it may be formed in a strip so as to extend over a plurality of pixels 7. As is seen from FIG. 13, the opposing electrode op is formed not only on a display area 11 in which pixels 7 are arrayed, but also over substantially the entire surface of the transparent substrate 10.
Again, in FIG. 14 and FIG. 15(A), the common feeder com is electrically connected to the other one of the source and drain regions of the second TFT 30 through a contact hole of the first interlayer insulating film 51. An extension 39 of the common feeder com opposes an extension 36 of the gate electrode 31 of the second TFT 30 with the first interlayer insulating film 51 as a dielectric film therebetween to form the storage capacitor cap.
However, in the active matrix display device 1A, since only the second interlayer insulating film 52 is interposed between the opposing electrode op facing the pixel electrode 41 and the data line sig on the same transparent substrate 10, which is different from a liquid crystal active matrix display device, a large amount of capacitance parasitizes the data line sig and the load on the data side drive circuit 3 increases.
Therefore, as shown in FIG. 13, FIG. 14, and FIGS. 16(A), 16(B), and 16(C), the present inventor suggests that by providing a thick insulating film (bank layer bank, a shaded region in which lines that slant to the left are drawn at a large pitch) between the opposing electrode op and the data line sig and the like, the capacitance that parasitizes the data line sig is decreased. At the same time, the present inventor suggests that by surrounding a region in which the organic semiconductor film 43 is formed by the insulating film (bank layer bank), when the organic semiconductor film 43 is formed of a liquid material (discharged liquid) discharged from an ink jet head, the discharged liquid is blocked by the bank layer bank and the discharged liquid is prevented from spreading to the sides. However, if such a configuration is adopted, a large step bb is formed due to the existence of the thick bank layer bank, the opposing electrode op formed on the upper layer of the bank layer bank is easily disconnected at the step bb. If such disconnection of the opposing electrode op occurs at the step bb, the opposing electrode op in this portion is insulated from the surrounding opposing electrode op, resulting in a dot defect or line defect in display. If disconnection of the opposing electrode op occurs along the periphery of the bank layer bank that covers the surface of the data side drive circuit 3 and the scanning side drive circuit 4, the opposing electrode op in the display area 11 is completely insulated from a terminal 12, resulting in disenabled display.
Accordingly, it is an object of the present invention to provide an active matrix display device in which, even when parasitic capacitance is suppressed by forming a thick insulating film around an organic semiconductor film, disconnection or the like does not occur in the opposing electrode formed on the upper layer of the thick insulating film.
In order to achieve the object described above, in the present invention, an active matrix display device includes a display area having a plurality of scanning lines on a substrates a plurality of data lines extending in the direction orthogonal to the direction of extension of the scanning lines, and a plurality of pixels formed in a matrix by the data lines and the scanning lines. Each of the pixels is provided with a thin film luminescent element having a conduction control circuit which includes a TFT in which scanning signals are supplied to a gate electrode through the scanning lines, a pixel electrode, an organic semiconductor film deposited on the upper layer side of the pixel electrode, and an opposing electrode formed at least over the entire surface of the display area on the upper layer side of the organic semiconductor film. The thin film luminescent element emits light in response to picture signals supplied from the data lines through the conduction control circuit. A region in which the organic semiconductor film is formed is bound by an insulating film formed in the lower layer side of the opposing electrode with a thickness that is larger than that of the organic semiconductor film, and the insulating film is provided with a discontinuities portion for connecting the individual opposing electrode sections of the pixels to each other through a planar section which does not have a step due to the existence of the insulating film.
In the present invention, since the opposing electrode is formed at least on the entire surface of the display area and opposes the data lines, a large amount of capacitance parasitizes the data lines if no measures are taken. In the present invention, however, since a thick insulating film is interposed between the data lines and the opposing electrode, parasitization of capacitance in the data lines can be prevented. As a result, the load on the data side drive circuit can be decreased, resulting in lower consumption of electric power or faster display operation. If a thick insulating film is formed, although the insulating film may form a large step and disconnection may occur in the opposing electrode formed on the upper layer side of the insulating film, in the present invention, a discontinuities portion is configured at a predetermined position of the thick insulating film and this section is planar. Accordingly, the opposing electrodes in the individual regions are electrically connected to each other through a section formed in the planar section, and even if disconnection occurs at a step due to the existence of the insulating film, since electrical connection is secured through the planar section which corresponds to the discontinuities portion of the insulating film, disadvantages resulting from disconnection of the opposing substrate do not occur. Therefore, in the active matrix display device, even if a thick insulating film is formed around the organic semiconductor film to suppress parasitic capacitance and the like, disconnection does not occur in the opposing electrode formed on the upper layer of the insulating film, and thereby display quality and reliability of the active matrix display device can be improved.
In the present invention, preferably, the conduction control circuit is provided with a first TFT in which the scanning signals are supplied to a gate electrode and a second TFT in which a gate electrode is connected to the data line through the first TFT, and the second TFT and the thin film luminescent element are connected in series between the opposing electrode and a common feeder for feeding a driving current formed independently of the data line and the scanning line. That is, although it is possible to configure the conduction control circuit with one TFT and a storage capacitor, in view of an increase in display quality, it is preferable that the conduction control circuit of each pixel be configured with two TFTs and a storage capacitor.
In the present invention, preferably, the insulating film is used as a bank layer for preventing the spread of a discharged liquid when the organic semiconductor film is formed in the area bound by the insulating film by an ink jet process. In such a case, the insulating film preferably has a thickness of 1 xcexcm or more.
In the present invention, when the insulating film is formed along the data lines and the scanning lines such that the insulating film surrounds a region in which the organic semiconductor film is formed, the discontinuities portion is formed in a section between the adjacent pixels in the direction of extension of the data lines, between the adjacent pixels in the direction of extension of the scanning lines, or between the adjacent pixels in both directions.
In a different manner from the mode described above, the insulating film may extend along the data lines in a strip, and in such a case, the discontinuities portion may be formed on at least one end in the direction of extension.
In the present invention, preferably, in the region in which a pixel electrode is formed, a region overlapping the region in which the conduction control circuit is formed is covered with the insulating film. That is, preferably, in the region in which the pixel electrode is formed, the thick insulating film is opened only at a planar section in which the conduction control circuit is not formed, and the organic semiconductor film is formed only in the interior of this section. In such a configuration, display unevenness due to the layer thickness irregularity of the organic semiconductor film can be prevented. In the region in which the pixel electrode is formed, in a region overlapping the region in which the conduction control circuit is formed, even if the organic semiconductor film emits light because of a driving current applied from the opposing electrode, the light is shielded by the conduction control circuit and does not contribute to the display. The driving current that is applied to the organic semiconductor film in the section which does not contribute to the display is a reactive current in terms of display. In the present invention, the thick insulating film is formed in the section in which such a reactive current should have flowed in the conventional structure, and a driving current is prevented from being applied thereat. As a result, the amount of current applied to the common feeder can be reduced, and by decreasing the width of the common feeder by that amount, the emission area can be increased, thereby display characteristics such as luminance and contrast ratio can be improved.
In the present invention, preferably, an active matrix display device includes a data side drive circuit for supplying data signals through the data lines and a scanning side drive circuit for supplying scanning signals through the scanning lines in the periphery of the display area; the insulating film is also formed on the upper layer side of the scanning side drive circuit and the data side drive circuit, and the insulating film is provided with a discontinuities portion for connecting the opposing electrodes between the display area side and the substrate periphery side through a planar section which does not have a step caused by the existence of the insulating film at the position between the region in which the scanning side drive circuit is formed and the region in which the data side drive circuit is formed. In such a configuration, even if disconnection of the opposing electrode occurs along the periphery of the insulating film that covers the surface of the data side drive circuit and the scanning side drive circuit, the opposing electrode on the display area side and the opposing electrode on the substrate periphery side are connected through the planar section which does not have a step caused by the existence of insulating film, and the electrical connection between the opposing electrode on the display area side and the opposing electrode on the substrate periphery side can be secured.
In the present invention, when the insulating film is composed of an organic material such as a resist film, a thick film can be formed easily. In contrast, when the insulating film is composed of an inorganic material, an alteration in the organic semiconductor film can be prevented even if the insulating film is in contact with the organic semiconductor film.